Redheaded Pine Sawfly Is Destructive

sawfly

Redheaded Pine Sawfly larvae may appear as caterpillars, but eat pines and cedars. Left unchecked, they can kill these common Wakulla County trees.

By Les Harrison
Wakulla County Extension Director

Looks, as the old saying goes, can be deceiving. This useful advice was certainly applicable to all the nocturnal visitors in the past week who were wearing Halloween costumes, but the recommendation is valid far beyond the much merchandised cultural event.

History is replete with examples of mistaken identity. These may be as comical as the greenhorn prospector who mistakenly identifies pyrite (fool’s gold) as the precious yellow metal or as serious as someone who is mistakenly branded a criminal.

This has been a problem for those who are attempting to recognize a specific insect group based on a single feature. The monarch butterfly and its mimic the viceroy butterfly are a well-known example.

Another lesser known example  is the sawfly larvae, which is frequently mistaken for a caterpillar. Some sawflies in Wakulla County are native insects with a well-deserved reputation for destructive behavior.

To entomologists, those people who spend their careers studying insects and other crawly creatures, the term caterpillar has a very specific meaning. Popular culture has converted this term into a brand, cartoons, and most tubular shaped bugs located on shrubs.

Only butterflies and moths, Lepidoptera, larvae are correctly classified as caterpillars. Among the more obvious characteristics are five or fewer pairs of pro-legs, those appendages extending from the base of its body.

Other traits include Y or V shaped cleavage lines on the head and a complex eye with six stemmata, for those who wish to look closer. There are other minute and specific identifiers, but these are often left to assess by professionals.

There are numerous sawfly species found in North America. The redheaded pine sawfly, Neodiprion lecontei, is one species found in Wakulla County which is native to the U.S., being found primarily east of the Great Plains and north into Canada.

Though similar in appearance to caterpillars, larvae have six pro-legs and simple eyes with only two stemmata. As their name implies, they do have a red head and they are commonly found on pine trees.

The redheaded pine sawfly is one of many sawfly species worldwide, including 35 in its specific genus. The term sawfly comes from the saw-like ovipositor which females use to deposit its eggs.

For the timber and landscape industry, this species is an economically important defoliator of commercially grown pines.

Unfortunately, its feeding and reproductive environment is enhanced in monocultures of shortleaf, loblolly, and slash pine, all of which are commonly cultivated in the southern U.S.

Adults are easily overlooked, being less than half an inch in length. The emerging larvae are usually the first sign a problem exists.

An adult female creates slits in a pine needle and lays one egg per slit. Needles that have eggs laid in them look spotted or banded with alternating green and yellow patches.

In approximately four weeks, larvae emerge and feed on the pine needles in large gregarious groups. In approximately four more weeks, larvae drop to the ground below the tree they were feeding on and begin to spin cocoons in the leaf litter or top layer of soil.

Young, open-growing pine trees less than 15 feet tall are especially vulnerable. While pines are preferred, larvae will feed on a cedar if the favored food source is exhausted.

A large infestation is capable of completely stripping small pine trees of foliage. Younger larvae eat the outer edges of pine needles leaving behind the central tissue which wilts and dies to creating the appearance of dried straw, making sawfly damage distinctive.

Older larvae eat the entire needle, and if complete defoliation occurs, groups of larvae will move to the nearest acceptable foodsource and continue feeding. When foliage becomes scarce, larvae will even feed on the soft bark tissue of defoliated trees.

Control methods are available, but an early start is the key to minimizing damage.

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